Because "Pieces de fantaisie pour orque Op.54/Carillon de West minster" aka "West Minster Chime" is the best carillon melody in the human history.
In Japan, the melody was used as the ear-catcher of radio news program during the WW2. After the war, a school in Tokyo started using the melody as its school bell. Some schools tried to find another unique chime melody, but none of them were as good as West Minster Chime.